San Francisco has equipped 30 buses with surveillance cameras to catch people parking illegally in transit-only lanes, and now Muni officials hope to expand the enforcement program to its entire fleet by the middle of next year.

The idea is to clear the path for Muni buses so they can get from one end of their run to the other without being slowed down by double-parkers and traffic congestion in lanes dedicated for transit.

"It's one way we can improve the running time," said John Haley, director of transit for the San Francisco Municipal Transportation Agency. Not a surprising goal, given that Muni operates at an average speed of 8 mph, making it among the slowest transit systems in the nation.

By increasing the average speed to just 9 mph, the city's chronically cash-strapped transit system could save an estimated $76 million a year by reducing the number of buses and drivers needed per shift. Muni's annual operating budget is $781 million.

It also could elevate Muni's anemic on-time performance rate, which has hovered below 75 percent - far below the 85 percent mark mandated by city voters 13 years ago.

The expanded camera program would dovetail into other proposals Muni is considering to speed service, including allowing more all-door boarding and eliminating some bus stops.

Another benefit of the transit-only-lane program, Haley said, is reducing the chance for bus-involved accidents because Muni drivers don't have to change lanes to avoid double-parked vehicles.

Currently, Muni has some designated transit-only lanes on blocks clustered in the Financial District, South of Market and Union Square areas. They cover about 15 miles of the city's 946 miles of surface streets. The transit-only lanes regulate portions of routes for 19 lines.

In addition to adding more cameras, city transit officials hope to make more traffic lanes off-limits to private cars and trucks. At the top of Haley's wish list for transit-only lane expansion: more blocks of Stockton Street, Geneva Avenue and Mission Street.

But for every block added to the transit-only program, there's one less block available for general use by other drivers. Haley said that supports San Francisco's Transit First policy, which encourages alternatives to driving.

San Francisco began the bus-lane camera program in 2008, with special permission from the Legislature and governor for a pilot project. The experiment, already extended once, is scheduled to run through the end of 2015.

The first year of the program resulted in the issuance of 1,311 citations. The number jumped to 2,102 the next year and to 3,052 the year after that.

"We've issued an increasing number of tickets, which isn't our goal," Haley said. "But they do get our message out that if you park in a transit-only lane we will see you."

The base fine for driving in a transit-only area is $60, and for parking in one is $105. In the past three years, $720,000 worth of fines have been issued, and the city has collected about 59 percent of that amount, Haley said.

The program works this way: Forward-facing cameras on the buses focus on the license plates of vehicles in transit-only lanes. Two parking control officers are assigned to review the images to determine whether a violation has occurred. The registered owners of the offending vehicles are mailed a citation. They can pay the fine or protest.

The cost to put cameras on all 819 buses in the Muni fleet would cost about $800,000, Haley said.